Redundancy and load balancing in a telecommunication unit and system

ABSTRACT

The invention relates to backing up a network element (NE) in a telecommunications system. The network element (NE) comprises at least two cluster nodes (A, B, C) that are redundancy units of each other. Each cluster node (A, B, C) contains virtual nodes (a 1 , a 2 , b 1 , b 2 , c 1 , c 2 ). Pairs are formed of the virtual nodes (a 1 , a 2 , b 1 , b 2 , c 1 , c 2 ) in such a manner that the first virtual node of the pair resides in the first cluster node and the second virtual node in the second cluster node. One of the virtual nodes in the pair is active and the other on standby. When a cluster node malfunctions, the virtual nodes of the pairs whose active virtual nodes reside in the faulty cluster node are interchanged by changing the standby virtual nodes to active and the active virtual nodes to standby.

BACKGROUND OF THE INVENTION

The invention relates to the redundancy of network elements and to loadbalancing in a telecommunications system, and especially to usingparallel gateway nodes, such as GGSNs (Gateway GPRS support node) in apacket-switched mobile system. To provide a concrete example, theinvention will be described in the context of a packet-switched mobilecommunication system.

The continuous development of applications transmitted in mobile systemssets ever increasing demands on mobile networks. An efficient use of theradio network determining the capacity of the system is important toenable extensive traffic. Packet-switched connections are more efficientthan circuit-switched connections in many applications. They areespecially well suited for burst data transmission, such as for the useof the Internet. A high bit rate is then required to load a new page,but, on the other hand, data traffic is almost non-existent when thepage is viewed. In circuit-switched connections, the capacity of theconnection is, however, all the time reserved for a certain user,whereby resources are wasted and the user must also pay for this. In apacket-switched system, resource allocation is based on the amount oftransmitted data and not the duration of the connection.

GPRS (General packet radio service) is a technique enablingpacket-switched data transmission that will be utilized in thethird-generation mobile network UMTS (Universal mobiletelecommunications system), for instance. GPRS requires the introductionof new network elements, such as GGSN, in the mobile system. GGSN is thenetwork element of the GPRS and UMTS mobile networks and controls therouting of data packets in the GPRS network and takes care of connectingthe GPRS network to other networks, such as the Internet and other GPRSnetworks.

In the GPRS system, the logical connection between a mobile station andGGSN supporting the mobile station is called a PDP (Packet dataprotocol) context. A redundant GGSN node comprises several GTP-U (GPRStunnelling protocol-User plane) and GTP-C (GPRS tunnellingprotocol-Control plane) processing units that apply packet transmissionbased on PDP contexts. Redundancy is used in the GTP-U and GTP-Cprocessing units to continue transmitting packets even in errorsituations. The redundancy is based on having a second processing unittake over, if the primary unit cannot continue transmitting packets. Theredundancy of network nodes, such as GGSN, is typically implementedusing backup units with a redundancy ratio of 1:1, whereby there is onebackup unit for each active unit. The problem with 1:1 redundancy isthat it makes the structure of the network node heavy and expensive, ifevery processing unit is to be backed up.

BRIEF DESCRIPTION OF THE INVENTION

It is thus an object of the invention to solve the problem. It is anobject of the invention to lower the hardware overhead to obtainredundancy. The object is achieved by developing a method and a systemimplementing the method and a network element that are characterized bywhat is stated in the independent claims. Preferred embodiments of theinvention are disclosed in the dependent claims.

The invention is based on using clusters, comprising parallel networkelement units, called cluster nodes, for backing up a network element,such as GGSN. A cluster node is an example of a GTP-U or a GTP-Cprocessing unit capable of serving PDP context activation requests.Processing units serve as backup units for each other. The cluster nodesinclude logical nodes that represent the pairs formed of the clusternodes in such a manner that a pair of logical nodes is associated witheach pair, and one of the logical nodes resides in the first clusternode and the other in the second cluster node. In the logical node pair,one of the logical nodes is active and the other is on standby. Adirected logical node pair, which indicates the active and standbylogical node, is referred to as a load allocation alternative.

GGSN redundancy is then based on the idea that when a user plane nodemalfunctions, the PDP contexts whose active logical node resides in thefaulty cluster node will be served by the standby logical node of thepair, which thereafter becomes the active logical node.

The method, system and network element of the invention provide theadvantage that 1:1 redundancy is not needed in the system and a pair canbe defined for each cluster node even if there is an odd number ofcluster nodes, for instance three. This way, when one cluster nodemalfunctions, only 33% of the PDP contexts need to be transferred to beserved by another cluster node assuming that the load of the networkelement is divided between three cluster nodes.

In one embodiment of the invention, the network load is balanced in sucha manner that when activating a PDP context, a logical node can beselected as the active node from the cluster node that has the leastload. This embodiment also provides the advantage that one solution isprovided for both network element load balancing and unit redundancy.This way, the system becomes resilient, i.e. has high availability andreliability. This is advantageous especially in a situation in whichonly a part of the sessions must have high availability. This embodimentis especially well suited for an environment comprising severalall-IP-GGSN (Internet protocol) units based on solely packet-switcheddata transmission, in which resiliency and availability are required ofthe system. A further advantage of this embodiment is that it alleviatesthe problem related to load balancing based on IP-based packettransmission, i.e. the fact that the transmission rate can decreasesignificantly when the load increases.

The invention also provides a combined resiliency solution for the GTP-Cand GTP-U processing units.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described in greater detail by means of thepreferred embodiments and with reference to the attached drawings, inwhich

FIG. 1 is a block diagram of a simplified system of the invention,

FIG. 2 is a schematic representation of external IP addressing of theinvention on the user plane,

FIG. 3 is a schematic representation of load balancing of the inventionon the user plane, when a high-speed internal switch is available,

FIG. 4 is a schematic representation of load balancing of the inventionon the user plane, when a high-speed internal switch is not available,

FIG. 5 is a schematic representation of external IP addressing of theinvention on the user plane and control plane,

FIG. 6 is a schematic representation of load balancing of the inventionon the user plane and control plane, when a high-speed internal switchis available,

FIG. 7 is a schematic representation of load balancing of the inventionon the user plane and control plane, when a high-speed internal switchis not available.

DETAILED DESCRIPTION OF THE INVENTION

The present invention can be applied to any telecommunications system inwhich network element redundancy is implemented using, together withactive units, standby units that can be activated when the active unitmalfunctions. These systems include third-generation mobile systems,such as UMTS (Universal mobile telecommunications system), and systemsbased on them, and the systems, such as GSM 1800 and PCS (Personalcommunications system), corresponding to the GSM system (Global systemfor mobile communications). The invention can also be applied to otherwireless systems and fixed systems.

In the following, the invention is described using an example systemthat is based on a 3GPP-all-IP system, without restricting the inventionthereto, however. 3GPP-all-IP is an IP technology-based system utilizingGPRS defined in the Third-generation partnership project 3GPP, in whichsystem network element redundancy is implemented using parallel backupunits.

FIG. 1 shows a simplified GPRS architecture that only shows the partsthat are essential for understanding the invention. It is apparent to aperson skilled in the art that a mobile system also comprises otherfunctions and structures that need not be described in detail herein.

The main parts of a mobile system are a core network CN, a radio accessnetwork RAN and a mobile station, also referred to as user equipment UE.The GPRS system uses a 3G radio access network (such as the UMTS radioaccess network) or a 2G radio access network (such as the GSM radioaccess network).

The GPRS core network CN can be connected to external networks, such asthe Internet. The main parts of the core network CN are a servinggateway support node SGSN and a gateway GPRS support node GGSN. The corenetwork described herein is based on the UMTS core network. Other typesof core networks, for instance IS-41, can comprise other networkelements.

The main functions of SGSN are detecting new GPRS mobile stations UE inits service area, processing the registrations of the new mobilestations UE, transmitting data packets to and from a GPRS mobile stationUE and maintaining a register on the locations of the mobile stations inthe service area.

The main functions of GGSN include interaction with an external datanetwork. GGSN connects the GPRS network of the operator to externalsystems, such as the GPRS systems of other operators, and data networks,such as the Internet. GGSN contains the PDP addresses of the GPRSsubscribers and routing information, in other words, the SGSN addresses.The SGSN-side interface of GGSN is called the Gn interface and the IPnetwork-side interface is called the Gi interface. The interface betweenSGSN and a network managed by another network operator PLMN2 (Publicland mobile network) is called the Gp interface. The operation of GGSNof the invention will be described later in connection with FIGS. 2, 3,4, 5 and 6.

The mobile station UE can be a speech-only terminal or it can be amulti-service terminal that serves as a service platform and supportsthe loading and execution of different functions related to services.The mobile station UE comprises actual mobile equipment and, typically,a detachably attached identification card, also called a subscriberidentity module, SIM. The mobile station can be any device or acombination of several different devices capable of communicating in amobile system. The subscriber identity module typically includes thesubscriber's identifier, executes authentication algorithms, storesauthentication and encryption keys and subscriber information requiredin the mobile station.

To transmit and receive GPRS data, the mobile station UE must activateat least one PDP context that it wants to use. PDP refers to a protocoltransmitting data in packets. This activation makes the mobile stationknown to the corresponding GGSN, and interworking with the network canbegin. A PDP context defines different data transmission parameters,such as the PDP address, quality of service QoS and NSAPI (Networkservice access point identifier).

A mobile station connected to a GPRS system can at any time start PDPcontext activation by transmitting an activate PDP context request toSGSN. After receiving the message, SGSN transmits a create PDP contextrequest to GGSN that creates the PDP context and transmits it to SGSN.SGSN transmits an activate PDP context acknowledgement to the mobilestation UE in response to a successful PDP context activation, afterwhich a virtual connection is established between the mobile station UEand GGSN. As a result, SGSN transmits data packets coming from themobile station UE to GGSN and GGSN transmits data packets received froman external network through SGSN to the mobile station UE. The PDPcontext is stored in the mobile station UE, SGSN and GGSN. Withoutrestricting it to the GPRS system, the PDP context is any logicalcontext that is established for the transmission of packet-switched databetween a terminal and the network element controlling the connection.One or more PDP contexts represent each PDP address in the mobilestation UE, SGSN and GGSN.

GTP (GPRS tunnelling protocol) refers to a protocol that is used totransmit user data between GPRS nodes in the GPRS core network. Two PDPcontexts on different interfaces and connected to each other form a GTPtunnel.

A system implementing the functionality of the present invention and itsnetwork element comprise not only prior-art means but also means forimplementing the functions described in more detail in connection withFIGS. 2, 3, 4, 5, 6 or 7. To be more specific, they comprise maintenancemeans for maintaining virtual cluster nodes in the cluster nodes, meansfor forming load allocation alternatives of said virtual cluster nodesand/or means for changing the load allocation. In addition, the networknodes can comprise means for distributing the load to active clusternodes, means for distributing the load of the network element betweenthe cluster nodes, means for distributing the load of the networkelement on the basis of a load allocation plan, means for defining anexternal IP address for the load allocation alternatives, means formaintaining information on a primary and secondary cluster nodeassociated with the load allocation alternative, switching means fortransmitting data by using the IP address defined for the loadallocation alternative and/or means for changing the load allocationinternally in the network element. It is also possible that the systemand its network nodes comprise all the above-mentioned means.

The present network nodes comprise processors and memory that can beutilized in the functions of the invention. All alterations required toimplement the invention can be performed as added and updated softwareroutines and/or using hardware-based solutions, such as ASIC(application-specific integrated circuit) circuits, or a separate logic.

In the following description, the terms ‘control plane’ (CP) and ‘userplane’ (UP) are used. All information transmitted and received by amobile station user, such as coded voice data in voice calls or packetsof an Internet connection, are transmitted on the user plane. Thecontrol plane is used for all control signalling related to the mobilesystem that is usually not visible to the user. There may be exceptionsto this, for instance short messages can be transmitted on the controlplane. On the radio interface, the control-plane and user-plane data canbe multiplexed to the same physical channel.

Implementation of the First Embodiment

The following describes, how the invention is implemented on the userplane.

FIG. 2 shows a network element NE, which is for instance a GGSN node.The network element comprises two or more physical GTP-U processingunits A, B, C, which are herein also called cluster nodes. The clusternodes A, B, C are capable of serving PDP contexts. The cluster nodes arearranged in pairs such that each cluster node can form a pair with everyother cluster node. For instance, if the number of available clusternodes N=3, the number of possible pairs P=3. If N=4, then P=6. In thesituation shown in FIG. 2, the number of cluster nodes N=3, and thepossible cluster node pairs are then AB, BC and CA. In each pair, thefirst cluster node is a backup unit of the second cluster node.

According to the present invention, the cluster nodes contain logicalnodes a1, a2, b1, b2, c1, c2, which are also called virtual clusternodes or virtual nodes. The number of virtual nodes is preferably twicethe number of the pairs formed of the cluster nodes. The virtual clusternodes a1, a2, b1, b2, c1, c2 are logical GTP-U processing units. Theyare arranged in pairs in such a manner that the first virtual node ofthe pair is active and the second is on standby. The same cluster nodecan comprise both active and standby virtual nodes.

A directed virtual node pair has a feature visible outside the networkelement called a load allocation alternative LBX1, LBX2, LBY1, LBY2,LBZ1, LBZ2, which is a logical Gn, Gp or Gi interface. Table 1 shows theload allocation alternatives for three processing units A, B, C, andillustrates which of the virtual nodes of the load allocationalternative is active and which is on standby.

TABLE 1 Virtual node Processing unit pair Load allocation alternativeActive Standby AB LBX1 a1 b2 LBX2 b2 a1 BC LBY1 b1 c2 LBY2 c2 b1 CA LBZ1c1 a2 LBZ2 a2 c1

Two or more virtual node pairs formed in an equal manner can havedifferent load allocation alternatives which may have other differencesapart from the formulation of the virtual node pair.

Each load allocation alternative has an external IP address that is usedas the user plane address of the PDP context. When a PDP contextactivation request is processed in GGSN, one of the load allocationalternatives is selected. A serving virtual node, i.e. active node, anda standby virtual node is selected. The selection is based for instanceon the load information of the cluster nodes or a specific alternatingdiagram.

If a cluster node A, B, C malfunctions, allocation of the PDP contexts,whose active unit this cluster node is, is changed. The active virtualnode serving the PDP context is put on standby and the correspondingstandby virtual node becomes active, unless it happens to be faulty aswell. In this description, the change of the active and standby unit isalso referred to as a ‘switchover’. When the corresponding standby unitsbecome active, they start serving the PDP contexts.

Each load allocation alternative has an individual external user planeIP address at the Gn or Gp interface for receiving the data packets thatarrive at GGSN. This individual address of the load allocationalternative is used as the PDP context address of the active virtualnode of the load allocation alternative. It is the feature of the loadallocation alternative that is visible at the external interfaces of thenetwork element. The IP address is used to indicate the route throughthe physical interface of the cluster node A, B, C.

The traffic in the network element NE may be distributed between thecluster nodes that comprise active virtual nodes on the basis of aspecific load allocation plan. The traffic in the network element NE maybe distributed between the cluster nodes that comprise standby virtualnodes, whereby the standby virtual nodes are made active.

Implementation of the First Embodiment Using an Internal Switch

FIG. 3 shows an implementation of the invention on the user plane, whenGGSN has a high-speed internal switch K or a corresponding connectionbetween the cluster nodes A, B, C. By means of the internal switch K,any alterations required to recover from faults can be hidden at theinterfaces of the network element, whereby the change of the activecluster node to the standby node and vice versa is not visible outsidethe network element NE. Packets arriving at the physical Gi interfaceGif or the Gn interface Gnf of the cluster node A, B, C are transmittedthrough the internal switch K to the active cluster node. For the sakeof clarity, FIG. 3 shows one switch K, but in reality, there may beseveral switches. Gnf could also illustrate the Gp interface.

According to a preferred embodiment of the invention, load allocation isbased on routing (routing-based link resiliency) protocols, in otherwords, information on a primary and secondary route to the loadallocation alternative is maintained inside GGSN. The primary route isthe physical interface of the cluster node comprising the active logicalnode of the load allocation alternative. The secondary route is thephysical interface of the standby unit. When activating a PDP context,the load allocation alternative is offered from a cluster node A, B, Cthat has available capacity. The physical Gn interface Gnf or physicalGi interface Gif, at which the packets arrive in the network node, neednot reside in the cluster node from which the load allocationalternative is offered. In other words, the packets can arrive at anyinterface and they are transmitted through the internal switch K of thenetwork node to the active cluster node. Forwarding information ismaintained in GGSN to enable indicating the primary and secondary routethrough the physical Gi or Gn interface of the cluster node to theactive unit. The load allocation change or a switchover between theactive unit and the standby unit is not visible outside the networkelement, because the external IP address of the load allocationalternative is the only address visible outside the network element.When the primary connection malfunctions, data packets are guided to usethe secondary route of the load allocation alternative. A fault in thefirst interface (for instance Gn) of GGSN is not visible to the secondinterface (for instance Gi).

According to another preferred embodiment of the invention, loadallocation is based on a link layer solution (link layer resiliency). Inthis case, too, the physical Gn interface Gnf or physical Gi interfaceGif need not reside in the cluster node A, B, C, in which the activeunit processes packets. In the link layer solution, a load allocationalternative has a physical interface dedicated for it, and the standbyunit monitors the physical connection or interface Gif, Gnf of theactive unit. Another GGSN component can also perform the task. If thestandby unit receives information on a malfunction of the interface usedby the active unit, the standby unit initiates the switchover. Thestandby unit then starts to use the backup interface instead of thededicated physical interface Gif, Gnf of the faulty unit, and packetsaddressed to the faulty unit are directed to the standby unit throughthe internal switch K. In this embodiment, too, a switchover or aninternal load allocation change of the load allocation alternative isnot visible outside the network element as a change in the external IPaddress but as a change in the address on the link layer, because the IPaddress of the load allocation alternative is the only routing addressvisible outside the network element. When the primary connectionmalfunctions, data packets are guided to use the secondary route of theload allocation alternative. A fault in the first interface (forinstance Gn) of GGSN is not visible to the second interface (forinstance Gi).

According to yet another preferred embodiment of the invention, theabove-mentioned solution based on routing and the solution of the linklayer can be applied simultaneously, in which case first a quickrecovery from the malfunction of the cluster node takes place based onthe link layer solution and then a recovery based on the routing.

The visibility of a load allocation alternative may be on both sides ofthe network element NE. This means that there may be a similar featureof the load allocation alternative on the Gi and the Gn side of GGSN.The external addressing of the load allocation alternatives may be basedfor instance on the subnet address range used for the PDP context IPaddresses, the IP tunnel endpoint address in case of a tunnelingmechanism (such as Generic routing encapsulation GRE, IP-in-IP, or IPsecurity protocol IPSec), or a set of label switched paths used by theload allocation alternative.

Methods for guiding data packets to use a secondary route to the loadallocation alternative in a routing-based solution or for starting theuse of an alternative physical interface in the link layer solution aredescribed later in ‘Changing of the physical interface’ of thisdescription.

Implementation of the First Embodiment Without an Internal Switch

FIG. 4 shows an implementation of the invention on the user plane, whenno high-speed internal switch is available in the network element. Theswitchover or the load allocation change is then not an internal networkelement change, but is visible outside. In other words, the routechanges on both interfaces Gn, Gi.

In yet another preferred embodiment of the invention, an integrated loadallocation change or switchover is performed. In a routing-basedsolution, data packets then arrive at the network element NE in such amanner that the external address of the load allocation alternative ismarked as their IP address. The primary routes for transmitting datapackets are the one that use the physical Gi interface Gif or physicalGn interface Gnf of the cluster node A, B, C, in which the active loadallocation alternative resides. When the cluster node malfunctions, thesecondary routes are used. When using the secondary routes, the packetsarrive at the physical interface of the cluster node, in which thesecond load allocation alternative resides and which then becomes theactive unit. The change of the route to the secondary route is visibleoutside the network element. Routing protocols can be used to indicatethe secondary route on the physical interface.

In an integrated load allocation change of yet another preferredembodiment of the invention, it is possible to use a link layer solutionthat is based on the idea that the standby unit of the load allocationalternative monitors the physical Gi interface Gif and physical Gninterface Gnf of the active unit. Another GGSN component can alsoperform this task. If an error is detected, the standby unit starts touse the alternative physical interface of the faulty unit. Methods forchanging the physical interface are described later in ‘Changing of thephysical interface’ of this description. The standby unit can then startto use the alternative physical interface, if it is the standby unit ofall the PDP contexts whose active unit the faulty unit is. This can beachieved by indicating routes on the physical interface of the standbyunit that replaced the faulty unit. Because the Gn-side changes alsoneed to be made on the Gi-side (and vice versa), a logical Gi interface(or Gn interface) is allocated for each load allocation alternative.

The routing solution or the link layer solution can be applied to the Giinterface regardless of which solution is applied to the Gn interface,and vice versa. Methods for guiding data packets to use a secondaryroute to the load allocation alternative in a routing-based solution orfor starting the use of the alternative physical interface in the linklayer solution are described later in ‘Changing of the physicalinterface’ of this description.

Implementation of the Second Embodiment

The following describes a combined user plane and control planeimplementation of the invention.

FIG. 5 shows a network element NE, which is for instance a GGSN node.The network element comprises two or more physical GTP-U processingunits A, B, C, which are herein also called user plane cluster nodes,and two or more physical GTP-C processing units D, E, F which are hereinalso called control plane cluster nodes. The user plane and controlplane cluster nodes A, B, C, D, E, F are capable of serving PDPcontexts. According to the second embodiment of the invention, servingpairs are formed of the user plane and control plane cluster nodes suchthat a user plane cluster node and a control plane cluster node form apair. In a serving pair, both of the nodes are active. Each user planecluster node can form a pair with every control plane cluster node andvice versa. The serving pair has a backup pair on standby. Each backuppair can be the backup pair of every serving pair. The backup pair alsocomprises a control plane cluster node and a user plane cluster node.

According to this embodiment, the user plane and control plane clusternodes comprise logical nodes, which are also called virtual clusternodes or virtual nodes a4, b4, d4, e4. The virtual nodes are logicalGTP-U or GTP- C processing units. The virtual nodes are arranged inpairs such that the first virtual node of the first pair resides in theGTP-U processing unit of the serving pair and the second virtual node ofthe first pair resides in the GTP-U processing unit of the backup pair,and such that the first virtual node of the second pair resides in theGTP-C processing unit of the serving pair and the second virtual node ofthe second pair resides in the GTP-C processing unit of the backup pair.The virtual node pairs are further arranged in secondary pairs such thatthe first virtual node pair resides in the GTP-U processing units andthe second virtual node pair resides in the GTP- C processing units.Table 2 shows the possible serving pairs and backup pairs for threeGTP-U processing units A, B, C and three GTP-C processing units D, E, F.

TABLE 2 UP processing units CP processing units Serving pair + Backuppair A, B D, E AD + BE AE + BD BE + AD BD + AE A, B E, F AE + BF AF + BEBF + AE BE + AF A, B F, D AF + BD AD + BF BD + AF BF + AD B, C D, E BD +CE BE + CD CE + BD CD + BE B, C E, F BE + CF BF + CE CF + BE CE + BF B,C F, D BF + CD BD + CF CD + BF CF + BD C, A D, E CD + AE CE + AD AE + CDAD + CE C, A E, F CE + AF CF + AE AF + CE AE + CF C, A F, D CF + AD CD +AF AD + CF AF + CD

The control plane virtual node d4, e4 and the user plane virtual nodea4, b4 of the backup pair may reside in different physical units even ifthe virtual nodes of the serving pair resided in the same physical unitand vice versa.

A directed secondary virtual node pair forms a load allocationalternative LB1. A directed secondary virtual node pair indicates whichare the active virtual nodes and standby virtual nodes associated withit. In the load allocation alternative LB1, user plane virtual node a4and control plane virtual node d4 are active, and user plane virtualnode b4 and control plane virtual node e4 are their standby virtualnodes.

Two or more secondary virtual node pairs formed in an equal manner canhave different load allocation alternatives which may have otherdifferences apart from the formulation of the secondary virtual nodepair.

Load allocation alternatives have external IP addresses that are used asthe addresses of the PDP contexts. The address may be different for userplane and control plane. When an activate PDP context request isprocessed in GGSN, load allocation alternatives for the user plane andcontrol plane are selected. When selecting a load allocation alternativethe (initial) serving pair and (initial) backup pair are selected. TheIP address of the user plane, e.g. IP address for cluster nodes A and B,and the IP address control plane, e.g. IP address for cluster nodes Dand E, are selected. The selection is based for instance on the loadinformation of the cluster nodes or on a specific alternating diagram.

If malfunctioning of a cluster node prevents a virtual node to continueas the active node, the backup virtual node is made the active node.This may be done separately on user plane and control plane. Aswitchover is thus performed. The active virtual node pair serving thePDP context is put on standby and the corresponding standby virtual nodepair becomes active, unless it happens to be in a faulty unit as well.When the corresponding standby units become active units they startserving the PDP contexts. Load allocation of the control plane clusternode does not necessarily have to be changed if the faulty unit is auser plane cluster node, and vice versa.

The routing address of the load allocation alternative is used as thePDP context address of the active virtual node of the load allocationalternative. It is the feature of the load allocation alternative thatis visible outside the network element. The IP address is used toindicate the route through the physical interface of the cluster node.

The traffic in the network element NE may be distributed between thecluster nodes that comprise active virtual nodes on the basis of aspecific load allocation plan. The traffic in the network element NE maybe distributed between the cluster nodes that comprise standby virtualnodes, whereby the standby virtual nodes are made active.

Implementation of the Second Embodiment Using an Internal Switch

FIG. 6 shows the implementation of the invention on the user plane, whenGGSN has a high-speed internal switch K or a corresponding connectionbetween the cluster nodes A, B, C, D, E, F. By means of the internalswitch K, any alterations required to recover from faults can be hiddenat the interfaces of the network element, whereby the change of theactive cluster node to the standby node and vice versa is not visibleoutside the network element NE. Packets arriving at the physical Giinterface Gif or the Gn interface Gnf of the cluster node A, B, C aretransmitted through the internal switch K to the active cluster node.For the sake of clarity, FIG. 6 shows one switch K, but in reality,there may be several switches.

According to a preferred embodiment of the invention, load allocation isbased on routing protocols (routing based link resiliency), in otherwords, information on a primary and secondary route to the loadallocation alternative is maintained inside GGSN. The primary route isthe physical interface of the cluster nodes comprising the serving pair.The secondary route is the physical interface of the cluster nodescomprising the backup pair. When activating a PDP context, the loadallocation alternative is offered from a cluster node pair that hascapacity available. The physical Gn interface Gnf or physical Giinterface Gif, at which the packets arrive in the network node, need notreside in the cluster nodes from which the load allocation alternativeis offered. In other words, the packets can arrive at any interface andthey are transmitted through the internal switch K of the network nodeto the active units. Forwarding information is maintained in GGSN toenable indicating the primary and secondary route through the physicalGi or Gn interface of the cluster node to the active units. Theswitchover or internal load allocation change of a load allocationalternative is not visible outside the network element, because the IPaddresses of the load allocation alternative are the only addressesvisible outside the network element. When the primary connectionmalfunctions, data packets are guided to use the secondary route of theload allocation alternative. A fault in the first interface (forinstance Gn) of GGSN is not visible to the second interface (forinstance Gi).

According to yet another preferred embodiment of the invention,allocation of PDP contexts is based on a link layer solution (link layerresiliency). In this case, too, the physical Gn interface Gnf orphysical Gi interface Gif need not reside in the cluster node pair, inwhich the active units process packets. In the link layer solution, aload allocation alternative has a physical interface dedicated for it,and the standby units monitor the physical connection or interface Gif,Gnf of the active units. Another GGSN component can also perform thetask. If the standby units receive information on a malfunction of theinterface used by the active units, the standby units initiate theswitchover. The standby units then start to use the backup interfaceinstead of the dedicated physical interface Gif, Gnf of the faulty unit,and packets addressed to the faulty unit are directed to the standbyunits through the internal switch K. In this embodiment, the switchoveror internal load allocation change of the load allocation alternative isnot visible outside the network element as a change in the external IPaddress but as a change in the address on the link layer, because the IPaddress of the load allocation alternative is the routing addressvisible outside the network element. When the primary connectionmalfunctions, data packets are guided to use the secondary route of theload allocation alternative. A fault in the first interface (forinstance Gn) of GGSN is not visible to the second interface (forinstance Gi).

According to yet another preferred embodiment of the invention, theabove-mentioned solution based on routing and the solution of the linklayer can be applied simultaneously, in which case first a quickrecovery from the malfunction of the cluster node takes place based onthe link layer solution and then a recovery based on the routing.

The visibility of a load allocation alternative may be on both sides ofthe network element NE. This means that there may be a similar featureof the load allocation alternative on the Gi and the Gn side of GGSN.The external addressing of the load allocation alternatives may be basedfor instance on the subnet address range used for the PDP context IPaddresses, the IP tunnel endpoint address in case of a tunnelingmechanism (such as GRE, IP-in-IP, or IPSec), or a set of label switchedpaths used by the load allocation alternative.

Methods for guiding data packets to use a secondary route to the loadallocation alternative in a routing-based solution or for starting theuse of an alternative physical interface in the link layer solution aredescribed later in ‘Changing of the physical interface’ of thisdescription.

Implementation of the Second Embodiment Without an Internal Switch

FIG. 7 shows an implementation of the invention on the user plane, whenno high-speed internal switch is available in the network element. Theload allocation change or a switchover is then not an internal networkelement change, but is visible outside. In other words, the route of thedata packets changes on both interfaces Gn, Gi.

In yet another preferred embodiment of the invention, an integrated loadallocation change is performed. In a routing-based solution, datapackets then arrive at the network element NE in such a manner that theexternal address of the load allocation alternative is marked as theirIP address. The primary route for transmitting data packets is the onethat uses the physical Gi interface Gif or physical Gn interface Gnf ofthe cluster nodes A, B, C, D, E, F in which the active load allocationalternative resides. When the cluster node malfunctions, the secondaryroute is used. When using the secondary route, the packets arrive at thephysical interface of the cluster nodes, in which the backup pairresides and which then become the active units. The change of the routeto the secondary route is visible outside the network element. Routingprotocols can be used to indicate the secondary route on the physicalinterface.

In an integrated load allocation change or a switchover of a preferredembodiment of the invention, it is possible to use a link layer solutionthat is based on the idea that the standby units of the load allocationalternative monitor the physical Gi interface Gif and physical Gninterface Gnf of the active units. Another GGSN component can alsoperform this task. If an error is detected, the standby unit starts touse the alternative physical interface of the faulty unit. Methods forchanging the physical interface are described later in ‘Changing of thephysical interface’ of this description. The standby unit can then startto use the alternative physical interface, if it is the standby unit ofall the PDP contexts whose active unit the faulty unit is. This can beachieved by indicating routes on the physical interface of the standbyunit that replaced the faulty unit. Because the Gn-side changes alsoneed to be made on the Gi-side (and vice versa), a logical Gi interface(or Gn interface) is allocated for each load allocation alternative.

The routing solution or the link layer solution can be applied to the Giinterface regardless of which solution is applied to the Gn interface,and vice versa. Methods for guiding data packets to use a secondaryroute to the load allocation alternative in a routing-based solution orfor starting the use of the alternative physical interface in the linklayer solution are described next in ‘Changing of the physicalinterface’ of this description.

Changing of the Physical Interface

When binding an IP address to a new link layer address in the situationsdescribed above, data packets may be lost. Methods for transmitting dataarriving at the network element NE to the physical Gi or Gn interface ofthe active cluster node A, B, C, D, E, F in the situations shown inFIGS. 3, 4, 6 or 7 without a packet loss are the forwarding, unicast andmulticast modes. Another benefit of these methods is that a dedicatedphysical interface is not needed.

The forwarding mode means that one of the cluster nodes serves as themaster to the group IP routing address of the network element or to theexternal address(es) of the load allocation alternative. The masterreceives the packets addressed to the group IP routing address or to theexternal address of the load allocation alternative and forwards them tothe active cluster node. The forwarding is based for instance on theload allocation alternative address of the data packet. If the mastermalfunctions, another master is selected in the network element, towhich packets addressed to the group IP routing address are thereaftertransmitted. The forwarding mode can be applied to the routing-basedsolutions described earlier in such a manner that the network elementeither has or does not have an internal switch available to it.

The unicast mode means that data arriving at the network element NE istransmitted separately to each cluster node, even though the data onlyhas one receiver. Each cluster node then receives the packet and eitheraccepts the packet or rejects it depending on the routing address(es) ofthe load allocation alternative of the data in question. The rejectionor the acceptance of the packet may be due the contents of the datapacket as well.

The multicast mode means that data can have several simultaneousreceivers. The data packet then arrives at the group IP routing addressof the network element, from which it is forwarded on in multicasting toall cluster nodes. Depending on the routing address(es) of the loadallocation alternative of the data, the cluster node either accepts orrejects the packet. The rejection or the acceptance of the packet may bedue the contents of the data packet as well.

Even though the invention is described above with the GTP- U or GTP- Cmanagement in GGSN as an example, it is apparent to a person skilled inthe art that the invention can also be applied to other protocols. Theinvention can also be applied to other cluster-implemented networkelements. Examples of other network elements, to which the invention canbe applied, are a serving GPRS node (SGSN), an IP base transceiverstation IP-BTS and a radio access network gateway RAN-GW.

Even though the invention is presented above by describing theredundancy of both the input and output interface and the loadallocation of the network element, it is apparent to a person skilled inthe art that the invention can also be applied to situations, in whichonly one of the interfaces is used.

It is apparent to a person skilled in the art that while the technologyadvances, the basic idea of the invention can be implemented in manydifferent ways. The invention and its embodiments are thus notrestricted to the examples described above, but can vary within thescope of the claims.

1. A method, comprising: maintaining one or more logical nodes in eachof first and second parallel physical cluster nodes configured totransmit data, wherein the first cluster node is a redundancy unit tothe second cluster node and vice versa, forming load allocationalternatives of the logical nodes, wherein the first logical node of theload allocation alternative resides in the first cluster node and thesecond logical node resides in the second cluster node, wherein thefirst logical node is active and the second logical node on standby orvice versa, and performing, when a cluster node malfunctions, aswitchover of the load allocation alternatives, the active logical nodesof which reside in the faulty cluster node, by changing their logicalnodes from standby to active and the active logical nodes to standby,wherein a network element in a communications system comprising thefirst and second cluster nodes is backed-up, the method also comprisingdefining an individual external routing address for each load allocationalternative, on the basis of which data is transmitted to the networkelement.
 2. A method as claimed in claim 1, wherein the load in thenetwork element is distributed between the cluster nodes that compriseactive logical nodes.
 3. A method as claimed in claim 1, wherein trafficin the network element is distributed between the cluster nodes thatcomprise logical nodes.
 4. A method as claimed in claim 1, whereintraffic in the network element is distributed on the basis of a specificload allocation plan between the cluster nodes that comprise logicalnodes.
 5. A method as claimed in claim 1, wherein information is furthermaintained on a primary and secondary cluster node associated with theload allocation alternative, wherein data is transmitted to the primarycluster node and after a switchover of a load allocation alternative,data is transmitted to the secondary cluster node of the load allocationalternative.
 6. A method as claimed in claim 1, wherein also aswitchover of a load allocation alternative is performed such that afterthe switchover, data is transmitted through a physical interface of thebackup cluster node to the redundancy unit of the cluster node.
 7. Amethod as claimed in claim 1, wherein the network element is backed upwithout a complete doubling of the number of the cluster nodes.
 8. Amethod as claimed claim 1, wherein said logical nodes aresoftware-associated components of the cluster nodes.
 9. A system,comprising: a network element that comprises at least first and secondparallel physical cluster nodes capable of transmitting data, whereinthe first cluster node is configured to serve as a redundancy unit tothe second cluster node and vice versa, wherein the system is configuredto maintain logical nodes at least in the first and second cluster node,form load allocation alternatives of the logical nodes such that thefirst logical node of the load allocation alternative resides in thefirst cluster node and the second logical node in the second clusternode, wherein the first logical node is active and the second on standbyor vice versa, and; perform, when a cluster node malfunctions, aswitchover of the load allocation alternatives, the active logical nodesof which reside in the faulty cluster node, by changing the logicalnodes from standby to active and the active logical nodes to standby,wherein the system is configured to define for each load allocationalternative an individual external routing address, on the basis ofwhich data is transmitted to the network element.
 10. A system asclaimed in claim 9, wherein the system is configured to distribute theload in the network element between the cluster nodes comprising activelogical nodes.
 11. A system as claimed in claim 9, wherein the system isconfigured to maintain information on a primary and secondary clusternode associated with the load allocation alternative, wherein data istransmitted to the primary cluster node and, after a switchover, data istransmitted to the secondary cluster node of the load allocationalternative.
 12. A system as claimed in claim 9, wherein the system isconfigured to perform a switchover of the load allocation alternative insuch a manner that after the switchover, data is transmitted through aphysical interface of the backup cluster node to the redundancy unit ofthe cluster node.
 13. A system as claimed in claim 9, wherein the systemis also configured to maintain information on a cluster node throughwhich the data is forwarded to the active cluster node.
 14. A system asclaimed in claim 9, wherein the system is also configured to transmitdata to one or more cluster nodes of the network element separately,wherein the cluster nodes either reject or receive the data based on arouting address of the load allocation alternative.
 15. A system asclaimed in claim 9, wherein the system is also configured to transmitdata to all cluster nodes of the network element in one go, wherein thecluster nodes either reject the data or receive the data based on arouting address of the load allocation alternative.
 16. A system asclaimed in claim 9, wherein the system is configured to back up thenetwork element without a complete doubling of the number of the clusternodes.
 17. A system as claimed in claim 9, wherein said logical nodescomprise software associated components of the cluster nodes.
 18. Anapparatus comprising: a first routine configured to maintain logicalnodes at least first and the second parallel physical cluster nodes,capable of transmitting data, whereby the first cluster node is aredundancy unit to the second cluster node and vice versa, a secondroutine configured to form load allocation alternatives of the logicalnodes such that the first logical node of the load allocationalternative resides in the first cluster node and the second logicalnode resides in the second cluster node, wherein the first logical nodeis active and the second on standby or vice versa, and a third routineconfigured to change, when a cluster node malfunctions, the loadallocation of the logical nodes of the load allocation alternatives, theactive logical nodes of which reside in the faulty cluster node, bychanging the logical nodes from standby to active and the active nodesto standby, wherein the apparatus also comprises a fourth routineconfigured to define an individual external routing address for eachload allocation alternative, on the basis of which data is transmittedto the network element.
 19. An apparatus as claimed in claim 18, whereinthe apparatus comprises a fourth routine configured to distribute theload in the network element between the cluster nodes that compriseactive logical nodes.
 20. An apparatus as claimed in claim 18, whereinalso comprises a fifth routine configured to distribute traffic in theapparatus between the cluster nodes that comprise logical nodes.
 21. Anapparatus as claimed in claim 18, wherein it also comprises a sixthroutine configured to distribute traffic in the apparatus on the basisof a specific load allocation plan between the cluster nodes thatcomprise the logical nodes.
 22. An apparatus as claimed in claim 18,wherein said first routine is also configured to maintain information ona primary and a secondary cluster node associated with the loadallocation alternative, wherein data is transmitted to the primarycluster node, and after a switchover, data is transmitted to thesecondary cluster node of the load allocation alternative.
 23. Anapparatus as claimed in claim 18, wherein the apparatus also comprisesan eighth routine configured to change load allocation wherein, afterthe switchover of a load allocation alternative, data is transmittedthrough a physical interface of the backup cluster node to theredundancy unit of the cluster node.
 24. An apparatus as claimed inclaim 18, wherein the apparatus also comprises a ninth routineconfigured to transmit data by using a routing address defined for theload allocation alternative even after a switchover of the loadallocation alternative.
 25. An apparatus as claimed in claim 18, whereinthe apparatus also comprises a tenth routine configured to perform aswitchover of a load allocation alternative inside the apparatus.
 26. Anapparatus as claimed in claim 18, wherein the apparatus comprises aneleventh routine configured to back up the apparatus without a completedoubling of the number of the cluster nodes.
 27. An apparatus as claimedin claim 18, wherein said logical nodes comprise software-associatedcomponents of the cluster nodes.
 28. An apparatus as claimed in claim18, wherein the apparatus is a gateway general packet radio servicesupport node.
 29. An apparatus, comprising: maintenance means formaintaining logical nodes at least in first and second parallel physicalcluster nodes capable of transmitting data, wherein the first clusternode is a redundancy unit to the second cluster node and vice versa,first forming means for forming load allocation alternatives of thelogical nodes such that the first logical node of the load allocationalternative resides in the first cluster node and the second logicalnode resides in the second cluster node, wherein the first logical nodeis active and the second on standby or vice versa, and execution meansfor changing, when a cluster node malfunctions, the load allocation ofthe logical nodes of the load allocation alternatives, the activelogical nodes of which reside in the faulty cluster node, by changingthe logical nodes from standby to active and the active nodes tostandby, wherein the apparatus also comprises a defining means fordefining an individual external routine address for each load allocationalternative, on the basis of which data is transmitted to the networkelement.
 30. An apparatus as claimed in claim 29, wherein the apparatuscomprises load allocation means for distributing the load in theapparatus between the cluster nodes that comprise active logical nodes.31. An apparatus as claimed in claim 29, wherein the apparatus alsocomprises load allocation means for distributing the traffic in theapparatus between the cluster nodes that comprise logical nodes.
 32. Anapparatus as claimed in claim 29, wherein the apparatus also comprisesload allocation means for distributing the traffic in the apparatus onthe basis of a specific load allocation plan between the cluster nodesthat comprise logical nodes.
 33. An apparatus as claimed in claim 29,wherein said maintenance means are also configured to maintaininformation on a primary and a secondary cluster node associated withthe load allocation alternative, wherein data is transmitted to theprimary cluster node and after a switchover, data is transmitted to thesecondary cluster node of the load allocation alternative.
 34. Anapparatus as claimed in claim 29, wherein the apparatus also compriseschanging means for changing load allocation in such a manner that afterthe switchover of a load allocation alternative, data is transmittedthrough a physical interface of the backup cluster node to theredundancy unit of the cluster node.
 35. An apparatus as claimed inclaim 29, wherein the apparatus also comprises switching means fortransmitting data by using a routing address defined for the loadallocation alternative even after a switchover of the load allocationalternative.
 36. An apparatus as claimed in claim 29, wherein theapparatus also comprises performing means for performing a switchover ofa load allocation alternative inside the network element.
 37. Anapparatus as claimed in claim 29, wherein the apparatus comprises backup means for backing up the apparatus without a complete doubling of thenumber of the cluster nodes.
 38. An apparatus as claimed in claim 29,wherein said logical nodes are software-associated components of thecluster nodes.
 39. An apparatus as claimed in claim 29, wherein theapparatus is a gateway general packet radio service support.
 40. Anapparatus, comprising: a processor configured to: maintaining logicalnodes at least in first and second parallel physical cluster nodescapable of transmitting data, wherein the first cluster node is aredundancy unit to the second cluster node and vice versa, form loadallocation alternatives of the logical nodes such that the first logicalnode of the load allocation alternative resides in the first clusternode and the second logical node resides in the second cluster node,wherein the first logical node is active and the second on standby orvice versa, and change, when a cluster node malfunctions, the loadallocation of the logical nodes of the load allocation alternatives, theactive logical nodes of which reside in the faulty cluster node, bychanging the logical nodes from standby to active and the active nodesto standby, wherein the processor is configured to define an individualexternal routing address for each load allocation alternative, on thebasis of which data is transmitted to the network element.
 41. Anapparatus as claimed in claim 40, wherein the processor is configured todistribute the load in the apparatus between the cluster nodes thatcomprise active logical nodes.
 42. An apparatus as claimed in claim 40,wherein the processor is configured to distribute the traffic in theapparatus between the cluster nodes that comprise logical nodes.
 43. Anapparatus as claimed in claim 40, wherein the processor is configured todistribute the traffic in the apparatus on the basis of a specific loadallocation plan between the cluster nodes that comprise logical nodes.44. An apparatus as claimed in claim 40, wherein said the processor isconfigured to maintain information on a primary and a secondary clusternode associated with the load allocation alternative, wherein data istransmitted to the primary cluster node and after a switchover, data istransmitted to the secondary cluster node of the load allocationalternative.
 45. An apparatus as claimed in claim 40, wherein theprocessor is configured to load allocation in such a manner that afterthe switchover of a load allocation alternative, data is transmittedthrough a physical interface of the backup cluster node to theredundancy unit of the cluster node.
 46. An apparatus as claimed inclaim 40, wherein the apparatus also comprises a switch configured totransmit data by using a routing address defined for the load allocationalternative even after a switchover of the load allocation alternative.47. An apparatus as claimed in claim 40, wherein the processor isconfigured to perform a switchover of a load allocation alternativeinside the network element.
 48. An apparatus as claimed in claim 40,wherein the apparatus comprises storage configured to back up theapparatus without a complete doubling of the number of the clusternodes.
 49. An apparatus as claimed in claim 40, wherein said logicalnodes are software-associated components of the cluster nodes.
 50. Anapparatus as claimed in claim 40, wherein the apparatus comprises agateway general packet radio service support.